1. Field
This application relates generally to a method of, and a system for, modifying the dynamic response of structures, and more particularly, to a method of, and a system for, increasing the energy dissipation capacity of structures.
2. Related Art
Most structures are subjected to dynamic excitation, or vibration, at some time. These vibrations may arise from wind, earthquake excitation, blast, machinery, or many other sources. The resulting vibrations may interact with the structure to induce inertial forces, which may result in a significant increase in structural loading. In some cases, especially under strong earthquake excitations, such vibrations may cause significant structural damage, or even collapse. In many cases vibrations may also affect the serviceability of a structure or the comfort of its occupants.
The dynamic response of a structure to such vibrations governed by several factors, among which, is the degree of energy dissipation that a structure can provide. This energy dissipation capability is often referred to as damping.
There are two principal sources of damping in conventional structures. The first is the so-called inherent, or intrinsic, damping from the materials comprising all of the elements of the structure. The second principle source of damping in structures comes from supplemental systems and devices, which modify the dynamic properties of the elements, or sometimes function as independent sub-systems within the structure.
It is often desirable, and sometimes necessary, to increase the energy dissipation capabilities of a structure, or individual elements of a structure. Others have proposed such means of providing supplemental damping for structures. Those skilled in the art will be familiar with the numerous so-called supplemental damping systems and devices currently in use. A description of some such systems and devices can be referenced from “Mitigation of Motions of Tall Buildings with Specific Examples of Recent Applications”, by Kareem, et. al. 1999 as well as from “Energy Dissipation Systems for Seismic Applications: Current Practice and Recent Developments”, by Symans, et. al. 2008. Reference is also made to the prior art described in “New Generation of Structural Concrete Systems for Seismic Resistance”, by Restrepo, 2006. The method and apparatus of prior art U.S. Pat. No. 4,417,427 issued to Bschorr Nov. 29, 1983 also attempts to achieve an increase in the energy dissipation capability, or damping, for concrete structural elements. All such prior art systems posses certain disadvantages:
(a) Where an energy dissipating means comprises an element that requires a space allocation beyond the extent of the structural elements, such space allocation may limit the architectural layout and function of the structure, and may require a sacrifice of valuable architecture. Further, such an intrusion may limit the architectural flexibility of the structure for future amended use.
(b) Where an energy dissipating means comprises an apparatus that is constructed within a structural element in such a way that the energy dissipating means is immediately engaged in its force-transmitting and energy dissipating function with the completed structural element, premature, unexpected or undesirable stress and strain in may occur in the energy dissipating means. Such residual stress and strain may result in permanent damage to the energy dissipating means, or otherwise render the damping means ineffective or inefficient for its intended purpose.
(c) Where an energy dissipating means comprises an apparatus that is constructed within a structural element in such a way that does not permit its removal and replacement at any time, there may be no way to modify or inspect the energy dissipating means after its installation. Similarly, where there is no way to install the energy dissipating means within a structural element, after construction of the structural element, it may not be possible to monitor the completed structure to determine the specific design requirements of the energy dissipating means, or weather such energy dissipating means is required at all.
(d) Where an energy dissipating means comprises an apparatus with an energy dissipation material means that is installed in-situ at a construction site, adequate quality assurance measures may not be possible.
Accordingly, it would be desirable to have an effective, reliable and controllable method and apparatus for increasing the energy dissipation of structures that overcomes the disadvantages associated with the prior art.
It is further desirable to provide an energy dissipating means that is internal to the structural element for which the energy dissipation is provided. Those skilled in the art will recognize the benefit of providing a non-obtrusive means that does not encroach, or otherwise interfere, with the use, or architectural flexibility, of the structure.
It is further desirable to permit the energy dissipating means to be installed, yet remain decoupled from the structure in its force resisting and energy dissipating function, until such time that it is desired to make it effective.
It is further desirable to permit the installation, removal, inspection, repair or replacement of the energy dissipating means to be made at any time during the life of the structure. Those skilled in the art will appreciate that in many situations, especially for earthquake design, it may be desirable, or even mandated, to be able to inspect, repair, or replace all or some portion of a supplemental energy dissipating means after a major earthquake. Similarly, it is desirable to permit the specific design requirements, or even necessity, of an energy dissipation means to be assessed during, or after, completion of the structure, and then implemented to address such requirements. Additionally, if there is a future change in the design requirements, such as by code mandate, or by design intent, it is desirable to have the capability to remove the original energy dissipation means and replace it with a new or modified energy dissipation means, having been so designed and modified to address any such new requirements.
It is further desirable to permit the application of any energy dissipation material means to be made under controlled conditions, and protected from exposure to damage during installation of the energy dissipation means into the structure